Nearly half of American Airlines' fleet of Boeing 757s -- 47 jets -- were taken out of service overnight and today as the troubled airline tried to make sure that no more of its coach seats came loose in flight, as they now have three separate times.

American said today that it had identified the reason that three of its flights had to be aborted midflight because of loose seats. In one case, passengers flipped on to their backs.

The seats come in rows of three, and the row is held to the floor with what's called a saddle clamp. It's that saddle clamp that was improperly installed on the planes where the seats disengaged.

The airline ruled out sabotage, saying it was either human or mechanical error. Many of its planes are now back in service.

One plane with loose seats flew for six days before seats were discovered, while another flew five days.

The last occurrence reportedly came loose on an American Airlines flight last week, a day after news first surfaced of loose seats on American Airlines flights that triggered two emergency landings in the span of three days.

The latest reported incident happened on a flight from Vail, Colo., to Dallas Sept. 26, the New York Post reported today.

The incident involved Flight 443 from New York's John F. Kennedy Airport to Miami Monday. The plane returned to JFK without incident when the seats were discovered, the Federal Aviation Administration said in a statement.

The earlier reported incident took place Saturday night when seats came unbolted on American Airlines Flight 685 from Boston to Miami. The flight was diverted and made an emergency landing at JFK.

The passengers in those seats were moved to other seats on the plane.

No one was injured and the aircraft landed safely at JFK. The passengers were delayed three hours before being put on another flight to Miami.

American says the investigation is still under way, but so far the airline cannot give a solid answer as to why the seats, which have been in use for up to 20 years, are coming loose now.

Aviation sources say the last eyes and hands on the saddle clamps in all three loose seat incidents belonged to company mechanics, which lead some to suspicions of possible sabotage, but safety experts tell ABC News that would be a first.

"To deliberately think that somebody would do something to a seat track assembly to cause it to come lose during flight is just something that's not thought of in this industry," said Kevin Hiatt, chief operating officer of the Virginia-based Flight Safety Foundation.

An airline representative said the airline does not believe the incidents are related to American's ongoing labor issues.

The mechanics union, which lost jobs to outsourcing, says it has had nothing to do with the loose seats and points to the new private maintenance.

The loose seats are just the latest serious labor troubles for American. The airline has suffered more than 2,200 delays and 75 cancellations in the last three days -- its planes have also been on time only 57 percent of the time.

"It's going to take American some time to rebuild trust in terms of the reliability of the schedule," Henry Harteveldt, airline and travel analyst at Atmosphere Research Group told ABC News.

The FAA said in a statement today that it was looking into the first two incidents and that the airline's initial inspection of each aircraft had found other rows of seats that were not properly secured.

"Preliminary information indicates that both aircraft had recently undergone maintenance during which the seats had been removed and re-installed," according to the FAA.

The FAA has stepped up scrutiny of American during its bankruptcy, as it has in the past for other carriers in similar situations. AMR Corp., American Airlines' parent company, filed for Chapter 11 bankruptcy in November 2011.